Which skin layer is the most superficial?

Correct Answer: B

Rationale: The stratum corneum is the most superficial skin layer, forming the horny, keratinized surface of the epidermis that protects against abrasion and water loss. The stratum lucidum, found in thick skin, lies just beneath it. The papillary and reticular dermal layers are in the dermis, below the epidermis, with the papillary being more superficial but still deeper than the corneum. As the outermost barrier, constantly shedding and renewing, the stratum corneum holds the top position in skin structure, making it the clear choice.

Correct Answer: C

Rationale: Vitamin D aids calcium uptake, is synthesized starting in the skin (UV converts 7-dehydrocholesterol), modified in the liver, and activated in the kidneys correct. It's a steroid hormone when active (calcitriol), also correct. However, it's not essential in the diet because the body can produce it via sunlight, making this statement incorrect. Dietary intake supplements natural production, but it's not required if UV exposure is adequate, a distinction in nutritional science that identifies this as the false claim.

Correct Answer: D

Rationale: Full-thickness burns over 20% destroy the epidermis and dermis, removing the waterproof stratum corneum, causing rapid water loss leading to dehydration and shock a primary life threat. Thermoregulation is impaired but secondary to fluid loss. Vitamin D loss isn't immediately fatal. Urea and uric acid excretion is minimal via skin (mostly kidneys), not a key issue. Water loss, a critical consequence of losing the skin barrier, is the dominant factor, as evidenced by burn treatment prioritizing fluid replacement.

Correct Answer: B

Rationale: Keratin, produced by keratinocytes, is the most common epidermal protein, filling the stratum corneum and providing strength and protection. Elastin is in the dermis for elasticity, not the epidermis. Melanin is a pigment, less abundant than keratin structurally. Cholesterol exists in cell membranes but isn't a dominant protein. Keratin's prevalence, forming the epidermis's tough outer layers, is a hallmark of skin histology, making it the correct answer.

Correct Answer: B

Rationale: The stratum corneum consists of dead, keratinized cells, forming a protective barrier shed through abrasion correct. Cell division occurs in the stratum basale, not corneum. Collagen, elastin, and reticular fibers are dermal, not in the avascular corneum. Sensory receptors reside in the dermis or deeper epidermis, not the dead corneum. Its dead cell composition is its defining trait, making this the accurate statement.